Are Makeup Mirrors Concave or Convex?

Makeup mirrors are concave. The magnifying side of a makeup mirror curves inward, like the inside of a spoon, and that curve is what makes your face look bigger. The non-magnifying side of a two-sided mirror is flat. Convex mirrors, which curve outward, make things look smaller and are never used for makeup.

That is the whole answer, but the curve explains a lot more than magnification: why the image goes blurry when you lean back, why you sometimes see yourself upside down, and why a stronger mirror makes you sit closer. If you are here because you are choosing one, my picks for the best lighted makeup mirrors all use a concave magnifying side.

Concave vs Convex Mirrors: What Is the Difference?

Both are curved mirrors, usually shaped like a slice of a sphere. The only difference is which side of the curve is silvered and facing you.

• A concave mirror curves away from you, like the bowl of a spoon. It gathers reflected light toward a point in front of the mirror, called the focal point.
• A convex mirror bulges toward you, like the back of the spoon. It spreads reflected light outward, as if it came from a point behind the mirror.

Why Are Makeup Mirrors Concave?

Because concave is the only curve that makes your face look bigger, and bigger is the point. When your face sits between a concave mirror and its focal point, the reflected light spreads out as if it came from a larger face standing behind the glass. Your eye sees that larger, upright image, and suddenly individual lashes, the edge of a liner and the stray hairs at the tail of a brow are easy to see.

No lens, coating or electronics are involved. The magnification is pure geometry: the deeper the curve, the shorter the focal length, and the stronger the effect. That is also why makers can put a 1x flat side and a 5x or 10x curved side back to back in the same frame.

How a Concave Mirror Magnifies Your Face

The focal length (f) is the distance from the mirror to its focal point. It is half the mirror's radius of curvature. For a concave mirror, the size of the upright image depends on how far your face is from the glass (d):

magnification = f ÷ (f minus d)

This is the standard mirror equation found in any introductory physics textbook. Two things fall out of it that matter at the vanity:

1. Magnification grows as you move toward the focal point. Right against the glass you see almost true size. As you back off toward f, the image gets bigger and bigger.
2. At the focal point it breaks down. The image becomes enormous and impossible to focus on.

An example with round numbers. Take a mirror with a focal length of about 8 inches, which is in the range I would expect for a 5x makeup mirror (makers rarely publish the figure). At 4 inches from the glass the formula gives 2x. At 6 inches, 4x. At about 6.4 inches, 5x. At 7 inches, 8x. At 8 inches, the image is gone. That is why the number on the box is a nominal figure: what you see depends on where you sit.

Why Does a Magnifying Mirror Go Blurry When You Lean Back?

Because you have crossed the focal point. Inside it, the mirror forms an upright image that your eye can focus on. Past it, the reflected light no longer spreads out from a point behind the mirror; it converges to form a real image in front of the mirror, upside down. Close to the focal point that image is huge and sits behind your own head, so your eye has nothing it can focus on and you see a blur of color.

Step back further, to around twice the focal length and beyond, and the image shrinks and lands between you and the mirror. Now your eye can focus on it, and you see yourself small and upside down. Try it with a magnifying mirror from across the room: the inverted little you is the same physics.

The practical rule: move in until the image is sharp, and stop before it blurs. Stronger mirrors have shorter focal lengths, so the sharp zone is closer to the glass. With a 10x side you are only a few inches away, which is exactly why I tell people to think hard before buying very high magnification. My guide to what magnification a makeup mirror should be gives approximate working distances for each level.

Where Convex Mirrors Belong, and Why Not on Your Vanity

Convex mirrors trade size for coverage. Because they spread light outward, they squeeze a wide scene into a small surface, which is perfect when you want to see a lot at once and terrible when you want to see detail.

• Car passenger-side mirrors. In the US, federal motor vehicle safety standard FMVSS 111 allows a convex mirror on the passenger side and requires it to carry the familiar warning that objects in the mirror are closer than they appear.
• Security and blind-spot mirrors in shops, parking garages and driveway exits.
• Hallway and stairwell corners in offices and hospitals.

At a vanity, a convex mirror would show your whole face and half the room, all of it smaller than life. That is the opposite of what you want for liner or brows.

Are Shaving Mirrors Concave or Convex?

The same rule applies. A magnifying shaving mirror is concave; a 1x shaving mirror is flat. Many fogless shower mirrors are flat or only mildly magnifying, because a strong concave curve would force you to stand very close to the wall under running water. If you shave in the shower, that is worth knowing before you buy one of the shaving mirrors I recommend.

How to Tell Which Kind of Mirror You Have

1. Bring your face close. If your reflection looks larger and upright, it is concave. Smaller and upright, convex. The same size, flat.
2. Step back slowly. A concave mirror will blur and then flip your reflection upside down. A convex mirror keeps you upright and just gets smaller.
3. Look at a straight edge. A door frame or tiled wall bends outward in a convex mirror and stays straight in a flat one.

Choosing a Concave Makeup Mirror

Once you know every magnifying makeup mirror is concave, the questions that separate a good one from a bad one are practical:

• Magnification level. Higher is not better. Most people do best with 5x for makeup and a stronger side only for brows. If you want a dedicated high-power mirror for tweezing or poor eyesight, see my best magnifying mirrors.
• Glass and grinding. A well-made curve gives a clean image right to the edge. A cheap curve, or a curved plastic surface, distorts toward the rim.
• Light. A concave mirror makes you sit close, and your head then blocks the room light. Built-in light solves that; I cover what kind in my guide to the best lighting for makeup.
• Two sides. A flat 1x side for the full face and a concave side for detail covers almost every routine.

Related: Best lighted makeup mirrors · Best magnifying mirrors · What magnification should a makeup mirror be? · The best lighting for makeup